Magnetic and dielectric study of R_0.5Sr_0.5MnO ₃ (R = Gd, Tb and Dy)

Magnetic and dielectric properties of perovskite manganites R _0.5Sr_0.5MnO₃ (R = Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at T_g ∼ 40 K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R³⁺ and Sr ³⁺ settled randomly at the same crystallographic site. Dielectric constants for each material were ∼1000-10,000 between ∼50 and ∼300 K and showed broad maximums above T_g. Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this sysstem are governed by the randomness at the R/Sr site. The tan δ and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3d electrons.